This invention relates to electrooptical devices. More particularly, it is concerned with electrooptical devices and methods for the rapid modulation and signal mixing of a collimated light beam.
Devices are known in the art which modulate a polarized light beam by means of the combination of a Kerr cell and a Glan-Thomson prism (see, for example, U.S. Pat. No. 3,501,220 to Bernal et. al.). These devices employ the Kerr effect to rotate the plane of a polarized light beam as it passes through an electrooptic cell to which an alternating electric field is applied. The light is then passed through the Glan-Thomson prism to deflect the light along one path or another depending upon the state of polarization. Devices of this type require relatively high voltages for their operation, typically of the order of several hundred volts.
Other light modulation devices are known in which a transducer physically moves one or more of the elements of the device to modulate the light beam (see, for example, U.S. Pat. No. 3,514,183 to Rabedeau). U.S. Pat. No. 4,165,155 to Gordon, II et al. discloses a device for modulating a collimated light beam employing an optically transparent element such as a prism separated from a smooth metal surface by a gap filled with a medium, such as air, having a refractive index less than that of the prism. A light beam passing through the prism is modulated by mechanically varying the spacing of the gap between the prism face and the smooth metal surface by means of, for example, a piezoelectric transducer. The frequency response of devices of the type where one or more elements of the system must be physically moved is limited by the rate at which the elements of the system can be mechanically oscillated.